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METABOLIC NETWORKS IN MONOLIGNOL (RADICAL RADICAL) COUPLING IN ARABIDOPSIS.  K.W. Kim, M.K. Kim, L.B. Davin and N.G. Lewis.  Institute of Biological Chemistry, Washington State University, Pullman.

   The arabidopsis genome consists of at least sixteen isovariants of the monolignol radical radical coupling proteins, defined as dirigent and dirigent-like proteins, respectively (Latin: dirigere, to guide and/or align).  One objective of the ongoing study is to define the physiological roles of each of the dirigent protein isovariants, including those of any related homologues awaiting discovery. Together, the 16 isovariants appear to constitute a comprehensive monolignol radical radical coupling network operative in different cells and tissue types during the life cycle of arabidopsis. Some of the genes are anticipated to encode proteins involved in lignan formation for plant defense, whereas others are presumed to harbor arrays of multiple dirigent (monolignol binding) sites considered to be involved in lignin biosynthesis. The 16 isovariants have 25-60% sequence identity to the Forsythia dirigent gene (GenBank AF210061).

   The experimental strategy employed thus far was designed to establish the spatial and temporal expression pattern of each of the 16 isovariants. This was achieved by constructing two sets of different expression plasmids consisting of 1) 16 equivalent dirigent promoter::gus plus::3ўflanking sequence::T-nos and 2) 16 equivalent dirigent promoter::mgfp::3ўflanking sequence::T-nos.  Transformation of each fusion plasmid into arabidopsis was carried out using hygromycin for selection. Molecular, biochemical and histochemical analyses of gus and gfp expression reveal further the expression patterns of the different isovariants during arabidopsis growth and development, i.e., in accordance with the existence of a complex network controlling monolignol radical radical coupling.

(Supported by NASA: NAG2-1513)

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